Air France acknowledged on Saturday that speed monitors on some of its Airbus planes have proven faulty, icing up at high altitude, and that recommendations to change them were first made in September 2007.
Air France issued a statement with details about the monitors hours after the French agency investigating the disaster of Fligh 447 said the instruments were not replaced on that aircraft - an A330 - before it crashed last week into the Atlantic Ocean en route from Rio de Janeiro to Paris.
Air France said it began replacing the monitors on the Airbus A330 model on April 27 after an improved version became available.
Pitot tubs, located on the exterior of the aircraft, are used to help measure aerodynamic speed.
Aviation officials have said the crash investigation is increasingly focused on whether external instruments may have iced over, confusing speed sensors and possibly leading computers to set the plane's speed too fast or slow - a potentially deadly mistake in severe turbulence.
An Air France statement said that cing of the monitors at high altitude has led at times to loss of needed flying information.
However, the Air France statement stressed the recommendation to change the monitor "allows the operator full freedom to totally, partially or not at all apply it." When safety is at issue the aircraft maker issus, rather than a recommendation, a mandatory service bulletin followed up by an airworthiness directive.
Air France said that only a "small number" of incidents linked to the monitors had been reported.
Airbus has said the French agency investigating the crash found the doomed flight received inconsitent airspeed readings by different instruments as it struggled with turbulence in a massive thunderstorm.